Conventionally, networks are deployed in tiered architectures utilizing a variety of transport media, e.g. optical fiber, wireless, coaxial cable, twisted pair, etc., and layers. Further, access, aggregation, long-haul, and other network types may use a variety of protocols, such as SONET, SDH, Optical Transport Network (OTN), and the like, as the underlying physical protocol. OTN is generally defined in various ITU-T recommendations, such as ITU-T Recommendation G.709 “Interfaces for the optical transport network (OTN).” OTN is capable of carrying synchronous, plesiochronous, or otherwise timed or untimed signals, but OTN does not carry any timing or synchronization in itself (i.e., OTN is asynchronous). Most networks are evolving to use Ethernet as a dominant transmission protocol, such as Gigabit Ethernet (GE), 10-Gigabit Ethernet (10GE), 100-Gigabit Ethernet (100GE), and other Ethernet variants. Ethernet is inherently asynchronous. More modern versions of Ethernet can be synchronous (Synchronous Ethernet referred to herein as “Sync-E”), at the physical level (i.e., G.826x series of standards such as g.8261, g.8264). However, building a useful network based on Sync-E requires all nodes along a chain to meet the Sync-E specifications. For example if a single node is not Sync-E compliant then Sync-E will not traverse that node and thus will not be available to further nodes. This is problematic as most currently deployed Ethernet devices (e.g., switches) do not support Sync-E nor do most new devices. For example, many network operators are looking to upgrade parts of their networks to the new technology but not the entire network.
Alternatively IEEE 1588 can be used to distribute timing. As described herein, IEEE 1588 or just “1588” is used to refer to IEEE 1588-2002, 1588v2-2008 Precision Time Protocol (PTP) standards and any variations thereof. PTP operates on the principle of timestamps applied to packets that are sent from a timing source (reference master) to a timing slave. Timestamps are applied in order to allow a slave to synchronize to a source. A receiver slave thus can recreate the original clock by reading these timestamps and adapting its own clock to them. (i.e., typical the source clock is stratum compliant and Building Integrated Timing Supply (BITS) referenced). Timing means both frequency and phase/Time of Day (ToD). However, switches in a network (between the source and slave) add timing jitter and delay due to traffic loading variations. Thus, timestamp corrections are added to a PTP packet, by the switches and by other network elements, as the PTP packet traverses the network in order to eliminate jitter introduced due to residence times in switch nodes. Note, the residence time of a packet in a switch node is not known ahead of time as it depends on a variety of factors, such as packet priority, switch load, egress port load, etc. As such, PTP requires specialized hardware support to timestamp packets entering and leaving the switch nodes. Thus, all nodes must include such support for PTP, but most conventional networks do not have PTP-capable nodes requiring a newly built network to support PTP. Operating PTP at some nodes and not others will result in clocking issues such as inability to reach the required stratum or other clocking requirements at the end node, long convergence times, and additional costs of the end node equipment (high stability local oscillator). Packet based syntonization (frequency only) requirements are detailed in the following standards: G.8261, G.8262, G.8263, G.8264. Synchronization requirements (phase and frequency with phase accuracy up to 1 usec) are included in;G.pactiming-bis, G.8265 (under study), TS 25.402, TS 36.300, TS 36.401, etc.
Equivalently to 1588 PTP, Network Time Protocol (NTP) (such as NTPv4 or other variants) may be used. NTP however is designed to work as a series of hierarchical nodes and is normally not expected to be as precise as PTP (for example it might be required to be precise to 100 milliseconds (ms) resolution or less such as 1 msec, instead of a few microseconds), and usually NTP is almost always implemented in software instead of hardware and is usually less precise than either Sync-E or PTP. A variety of applications are run over Ethernet such as voice, two-way video, and the like that have absolute time requirements in addition to jitter and wander specifications (exemplary specifications and requirements include G.823/G.824 and G.8261/G.8264, Bellcore GR-1244 etc). Thus, there exists a need for improved Ethernet synchronization systems and methods that overcome the above listed deficiencies.